1. Field of the Invention
The present invention relates to an image processing method for an imaging apparatus that uses a solid-state imaging device.
2. Description of the Related Art
An analog front end (AFE) is widely used. The AFE includes correlated double sampling (CDS) that removes noise from a signal outputted from a charge coupled device (CCD) imaging device; dark current correction; automatic gain control (AGC); and an analog digital converter (ADC) that converts the signal to a digital video signal Vi. The ADC grayscale of the AFE is conventionally 10 bits, but 12 bits and 14 bits have become common. Furthermore, there has been advanced improvement in a complementary metal oxide semiconductor (CMOS) imaging device that allows high-speed reading by integrating a drive circuit and a read circuit.
Furthermore, with the advancement of integration of a digital signal processing circuit, not only a memory-integrated digital signal processor (DSP) dedicated for video, but also an inexpensive, generic field programmable gate array (FPGA) can easily implement the storing of output signals from a plurality of lines and the performing of arithmetic processing. Megapixel cameras with over one million pixels, high definition television (HDTV) cameras, high-speed imaging HDTV cameras, HDTV cameras with a recording unit, HDTV cameras with an Internet Protocol (hereinafter, IP) transmitting unit, ultra-high definition televisions (UHDTVs) for higher definition 2K×4K cameras or 4K×8K cameras, and uncompressed recording apparatuses using a hard disk drive (HDD) have also been put into commercial production. In two-dimensional video display apparatuses, too, there has been advancement in higher definition 2K×4K or 4K×8K UHDTV display, high-speed display, and ultra-slimming down.
Since the refractive index of a lens varies depending on the wavelength of light, the focal length also varies depending on the wavelength of light. Since the focal length of a lens varies depending on the wavelength, there occur axial chromatic aberration where the position of an image plane is shifted back and forth depending on the color, and magnification chromatic aberration where the magnification of an image varies depending on the color and thus the size of an image varies depending on the color.
In addition, due to spherical aberration where the position in an optical axis direction of the focal point varies depending on the distance of an incident point from an optical axis, the modulation factor of the entire screen is reduced. Due to coma aberration where light emerging from one point outside the optical axis does not converge to a single point on the image plane, the modulation factor of an area on the periphery of the image is reduced. Furthermore, due to astigmatism where an image point in a concentric direction and an image point in a radial direction by a ray of light emerging from one point outside the optical axis are shifted from each other, the modulation factor of an area on the periphery of the image is reduced.
The spherical aberration is proportional to the third power of the numerical aperture (NA), and is irrelevant to the size of the field of view, and is the one and only aberration that appears even at the center of the screen. The spherical aberration of a lens doublet composed of two lenses in which the refractive index of a concave lens is higher than that of a convex lens is reduced by one digit or more over a single lens. In addition, the coma aberration is proportional to the second power of the open area ratio NA which is the reciprocal of the aperture ratio F, and to the first order of the size of the field of view. In addition, the astigmatism is proportional to the first order of NA and to the second order of the size of the field of view, and the modulation factor is reduced by the astigmatism particularly in an area on the periphery of the image.
A phenomenon where light collected by a lens does not focus on a single point is called aberration, and a lens that is corrected for spherical aberration and coma aberration among aberrations is called an aplanat, and furthermore, a lens in which a focal position shift caused by the wavelengths of light differing from each other is corrected at two locations, i.e., the red C-line (656.3 nm) and the blue F-line (486.1 nm), is called an achromat which is an achromatic lens. A lens that satisfies conditions that, for example, chromatic aberration is corrected at three wavelengths where the violet g-line (435.8 nm) is further added, and spherical aberration and coma aberration are corrected at two wavelengths is named as an apochromat by Abbe. A lens that is also corrected for astigmatism and that maintains both a circumferential direction modulation factor and a radial direction modulation factor is large in size and too expensive.
A lens that is not even an aplanat due to its insufficient correction of spherical aberration and that has a reduced modulation factor even at the center of the screen is insufficient in performance for UHDTVs. A lens in which coma aberration is insufficiently corrected and both of a circumferential direction modulation factor and a radial direction modulation factor are reduced is insufficient in performance for UHDTVs unless the circumferential direction modulation factor and the radial direction modulation factor are individually made changeable.
Meanwhile, an example of a DX standard macro which is a unifocal lens is the same as the wide angle of a zoom lens. In addition, an example of a DX standard macro which is a unifocal lens is the opposite of the telephoto of a zoom lens. In addition, an example of an FX medium telephoto which is a unifocal lens is the opposite of the wide angle of a zoom lens. Remaining aberration varies depending on different aberration correction methods.
Meanwhile, the applicant discloses a technique in which an imaging apparatus including a lens, an imaging device, and a video signal processing circuit having a contour correction function includes eight or more line memories, and generates a vertical contour correction signal from each of a plurality of video signals which are delayed by an integer horizontal period. In addition, the applicant discloses a technique in which the imaging apparatus has eight or more pixel delay functions, and generates a horizontal contour correction signal from each of a plurality of video signals which are delayed by an integer pixel quantity. Upon checking, the vertical contour correction signals and the horizontal contour correction signals are added to the video signals (see Patent Literature 1).
FIG. 5 is a block diagram showing an overall configuration of a conventional imaging apparatus. In FIG. 5, 1: a lens, 2: an imaging unit, 7: an imaging apparatus, 8: a signal processing unit, and 9: a CPU including a location-on-the-screen control unit. The signal processing unit 8 performs a contour enhancement process as shown in Patent Literature 1.
In addition, there is also an imaging apparatus that performs an image sharpening process such as an aperture correction process or an edge enhancement process only for a concentric direction of an image having been subjected to distortion aberration correction by image processing, and does not perform the image sharpening process for a radial direction of the image (see Patent Literature 2).